What is the main difference between a G Protein, a secondary messenger, and a relay molecule?
A. This is a tough one and I don’t think you really need to know this level of detail. I’ll give it a go. Again, depending on the source of information, you will find differences between how these three terms are all related. In relation to signal transduction, relay molecules are those involved in the signal transduction pathway, ie after the hormone-receptor complex has formed up to but not including the final molecule that is produced. So, this means that G-proteins and second messengers are examples of relay molecules. Second messenger systems (there appear to be three types, one of which is cAMP) involve relay molecules that tend to have an amplified effect, ie they stimulate a number of other relay molecules as a result of the initial hormone-receptor interaction. Whether G-proteins are an actual second messenger, I am not sure but I don’t think they are (some textbooks say they are). They are certainly part of signal transduction for non-steroid hormones because they are the rel
